The present invention relates to a sickle cutting apparatus which generally comprises a sickle bar mounted in transversely extending position and driven for reciprocating movement relative a set of guard fingers where the sickle bar has a plurality of knife blade sections mounted thereon with first and second side cutting edges to cooperate with shearing edges of the guard guards. Each of the knife guards has a base portion for mounting on the cutter bar and at least one guard finger mounted on the base portion so that the fingers are arranged in a row along the cutter bar with a space between each finger and the next allowing crop to enter the space up to a position of engagement with a rear trash bar. Each of the knife guard fingers has an upwardly facing ledger surface with opposed side edges to provide first and second shearing edges. Typically each of the guard fingers has a downwardly facing ground engaging surface shaped and arranged to provide protection for stone engagement. A hold down arrangement on top of at least some of the guard fingers acts to prevent lifting of the blades away from the guard surface.
Two methods have commonly been used to fasten knife sections to the sickle bar otherwise known as the knife-back.
Many years ago, the sections were normally fastened to the knife-back by means of rivets. To replace a section, the rivet heads were normally sheared off, the rivets pushed out, and a new section installed with new rivets. Some tools have been developed to facilitate this, but the process remained too labor intensive and inconvenient.
A more acceptable method of securing the sections which is commonly used today is to use threaded hardware. A common style of bolt used in the industry is a knurled bolt which is pressed into the knife-back. The knurls provide the “press fit” between the bolt and the knife-back. To replace a section when the hardware is still intact, the threaded nuts are removed, the old section lifted out and replaced, and the nuts are replaced. Depending on the style of guard and hold-down used, it is generally necessary to remove or at least loosen a guard or hold-down so that the section can be lifted out. In some other cases, the bolts can be pushed out so that the knife section can be slid out.
The term “sickle bar” as used herein is intended to refer generally to a structure which supports all of the blade sections at the spaced positions along its length and is not intended to be limited to a single continuous element extending along the whole length of the structure. Thus the bar may be formed of different elements at different parts of the length and may include pieces below and above the blade sections.
Pointed guards generally feature a point with a cut slot that the sickle sections reciprocate through. Various types of hold-down arrangement are used to apply pressure to the sickle to keep its shearing surface in close contact with the guard ledger as cutting occurs. Usually these are located between the guard points or at the rear edge of the sickles. Most are sheet metal and are typically adjusted using a hammer or a simple single point threaded adjustment. By keeping the hold-downs separate from the guards fewer hold-downs than points may be used to reduce the cost and number of adjustments required. Pointed guards have found much favor in easier cutting conditions due to the ease of adjustment and superior performance.
Another form of guard is known as a stub guard which is formed in two separate pieces including a base piece which carries the ledger surface and a top piece which extends over the ledger surface. The pieces are separate and separately adjustable relative to the cutter bar so that the top piece can apply pressure onto the blade portion to press it onto the ledger surface. The pieces terminate at a front edge which is just behind the front edge of the blade portion so that the front edge of the blade portion is presented to the crop.
In tough cutting, stub or no-clog guards have found the most favor. Stub guards use a separate top and bottom guard pieces that spaced slightly more than one sickle thickness apart create a slot for the sickle to operate in. The front edge of the sickle section protrudes slightly past the front tip of the two guard sections. This feature is what originally gave stub-guards their non-clogging self-cleaning action. A major improvement in stub guard technology was made when fully adjustable top hold-down assemblies were introduced. These arrangements allowed the gap to be controlled much more precisely than previously so that the shearing surface of the blade portion was kept in close contact with the guard ledger surface. This adjustability allows the stub top piece to act as a much more effective hold-down than the hold-downs found on regular pointed guard systems.
The pointed guard has an advantage of presenting a point to the incoming crop so that crop is effectively divided around it. This is especially advantageous when the sickle blade is at or near the end or start of each stroke and the blunt front edge of each blade or section is hidden partially or entirely within the guard slot. Since the sickle bar velocity is lowest at or near the end or start of each stroke this gives the pointed guard a considerable advantage.
The guards can be formed as single elements separately mounted on the guard bar or as double or triple elements connected together side by side for common mounting and common adjustment relative to the guard bar. There is no reason why more elements might be included but this is not typical.
In some cases the arrangement is of the double sickle type where each sickle bar is essentially half the length of the cutter bar and the cutter bars reciprocate in opposite phase to minimize vibrating mass and vibrations. Usually the sickle bars are timed so that they move in opposite directions so that vibrations induced into the cutter bar assembly are minimized.
The sickle knife cutting system has been widely accepted as the most power efficient system due to the shearing action. However due to speed restrictions of generally less than 5 to 8 mph ground speed, other systems such as rotating flail systems have come into use since these can be operated at much higher ground speed of up to 14 mph while maintaining a high cutting efficiency. Such rotary systems have however much higher power usage, are limited in width and provide crop handling difficulties for forming effective swaths for drying of the crop.